For all types of substrates, perpendicular magnetic recording (PMR) technology has become more prevalent in magnetic recording media with the goal of increasing areal density. Areal density is generally limited by the media's ability to, at a sufficiently small bit size, write a data bit, read back the same data bit, and maintain the magnetic characteristics of the data bit over time. For magnetic media, these parameters are controlled by the materials coercivity. However, there exists a threshold wherein the coercivity is so high, and the bit size so small, that the writing element must use an impractically high magnetic field to affect change to a data bit. The advent of heat-assisted magnetic recording (HAMR) media addresses this problem by applying heat to a data bit during a write operation to lower the coercivity to a writable level, and then removing the heat to allow the coercivity to return to a high level to keep the data bit stable.
By using HAMR technology, areal density in hard disk drives can be extended beyond 1 Tb/in2. FIG. 1 illustrates a HAMR head light delivery system design. Laser light from an external laser diode (LD) 100 is coupled into interferometric taper waveguide (I-TWG) 200 by mode converter (MC) 210, and then delivered through I-TWG 200 to near field transducer (NFT) 250 at air bearing surface (ABS) 270, which focuses the laser generated light energy into a less than 50 nm spot on the PMR media surface.
The structure of an I-TWG 200, as shown in FIG. 2, includes several critical components including mode converter taper 210, splitter 220, and directional coupler 230. Constructing these components into a unified structure on a single wafer with homogenous deposition and etching technologies is challenging because the components have very different dimensional scale, but dimensional accuracy is extremely important to operational performance of the HAMR. For example, the I-TWG taper angle and length, waveguide critical dimension uniformity (CDU), line edge roughness (LER), splitter asymmetry, and MC-to-taper overlay are critical to the HAMR's signal-to-noise ratio (SNR), head longevity, and power consumption. Directional coupler 230 is used to return some of the laser light to the backside of slider 150 (as shown in FIG. 1) for laser alignment adjusting. However, dimensional accuracy necessary to control the taper angle and length, CDU, LER, splitter asymmetry, and MC-to-taper overlay is difficult to control, particularly when building the I-TWG on a single substrate. Accordingly, currently available I-TWG methods tend to use more expensive, multi-substrate construction and tend to result in structures with variances in these critical parameters. The resulting I-TWG's are not ideal in their efficiency, power consumption, and head life.